**1. Introduction**

Winemaking is a complex process that extends from grape cultivation and harvesting to wine consumption. In the course of this process, many different chemical, physical, microbiological, and sensory reactions are involved. Microorganisms play an essential role, since alcoholic fermentation and frequently also malolactic fermentation are fundamental steps in winemaking. During these fermentation steps, the evolution of certain chemical compounds depends directly on their interaction with microorganisms, thereby resulting in many of the characteristic and desirable flavors in wine [1]. Conversely, microorganisms can also contaminate and spoil the wine in several steps of the winemaking procedure, causing refermentation, off-flavors, volatile acidity, and bottle explosion. Moreover, microorganisms can produce compounds that are hazardous for human health, such as biogenic amines [2]. The ultimate quality of wines and their commercial value are therefore directly associated with those microflora which are beneficial; nevertheless, microbial spoilage of wine can lead to a number of drawbacks and economic losses for the wine industry. It is thus essential to monitor the entire winemaking process in the endeavor to avoid contamination caused by microorganisms. This can be achieved using chemical preservatives and/or certain physical treatments designed to inactivate microorganisms, inhibit their growth, or directly separate them physically from wine.

The main yeasts regarded as true spoilage strains in wine are *Brettanomyces bruxellensis*, *Zygosaccharomyces bailii*, and *Saccharomyces cerevisiae*. *B. bruxellensis* is one of the most undesirable strains in wineries, as even at very low concentrations it can produce the typical "horse sweat" taint, and early detection is difficult [3]. Because of its tolerance to high sugar and sulfur dioxide concentrations, *Zygosaccharomyces* may cause turbidity, produce CO2, and even re-ferment sweet wines and grape juices [4]. *S. cerevisiae*, although involved in the alcoholic fermentation process, can be responsible for wine spoilage when a nutritional imbalance in the grape juice triggers off-flavor production. Other species of the genera *Kloeckera/Hanseniaspora*, *Pichia*, and *Candida* can also produce film layers and undesired metabolites [5].

Lactic Acid Bacteria (LAB) are responsible for malolactic fermentation (MLF), but can also negatively affect the quality of wines as spoilage microorganisms when they proliferate at the incorrect time during winemaking [6]. Wine-associated microbial LAB genera are *Lactobacillus, Leuconostoc, Oenococcus*, and *Pediococcus*. LAB growth in wine can imply the production of undesirable aroma and flavor compounds, biogenic amines, acrolein, and ethyl carbamate, or can cause a slimy appearance. In the category of Acetic Acid Bacteria (AAB), the three main associated genera considered as spoilage bacteria in wines are *Acetobacter*, *Gluconobacter*, and *Gluconacetobacter*. Their principal effect on wines is the production of acetic acid, acetaldehyde, and ethyl acetate, which confer sour, nutty, and solvent-like flavors, respectively. All these groups of spoilage microorganisms in wine have in common their ethanol tolerance, their ability to grow at low pH (< 4.0), and, in some cases, a high tolerance to SO2. In order to establish a methodology for must or wine decontamination and stabilization, it would be necessary to establish which are the target microorganisms in the different steps of winemaking, and to study their tolerance/resistance to the chosen lethal agent.
